Summary

A recently published Forest Service report examines the effect of climate change on forest diseases and how these pathogens will ultimately affect forest ecosystems in the Western United States and Canada. A Risk Assessment of Climate Change and the Impact of Forest Diseases on Forest Ecosystems in the Western United States and Canada explains fundamental relationships between tree diseases and climate conditions that will help land managers and others determine how local conditions may influence tree survival.

Drawing on a large body of published research, the report details the effects of eight forest diseases under two climate-change scenarios—warmer and drier conditions and warmer and wetter conditions. The forest diseases discussed in the report include foliar diseases, Phytophthora diseases (such as sudden oak death), stem rusts, canker diseases, dwarf mistletoes, root diseases, and yellow-cedar decline. The likelihood and consequences of increased damage mortality to forests from each disease as a result of climate change were analyzed and assigned a risk value of high, moderate, or low.

The scientists predict Armillaria root disease will cause the greatest risk to forest ecosystems under warmer and drier drought conditions. Armillaria is common on conifers and some hardwoods; it lives on tree roots and grows exponentially when a tree becomes stressed. Yellow-cedar decline, Cytospora canker on Aspen, and dwarf mistletoes also pose high risk under drought conditions. Sudden oak death and other Phytophthora tree diseases are likely to be most damaging under wetter and warmer conditions.

These deadly pathogens reproduce and spread quickly under favorable moist and warm conditions. Tree diseases shape America's forests, according to the scientists. Understanding how climate change will affect the diseases is paramount to sustaining healthy forests.